Gate driver for a fingerprint sensor

ABSTRACT

An example gate driver for an array of sensing pixels is disclosed. The gate driver includes a first flip-flop including a first data input and a first data output. The first data output is coupled to a first group of sensing pixels of the array. The gate driver also includes a second flip-flop including a second data input and a second data output. The second data output is coupled to a second group of sensing pixels of the array. The gate driver further includes a first insertion circuit configured to receive a first start signal and to cause, based on the first start signal, the second flip-flop to drive the second group of sensing pixels without the first flip-flop driving the first group of sensing pixels for a scan of the array.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority and benefit under 35 USC § 119(e) toU.S. Provisional Patent Application No. 62/658,381, filed on Apr. 16,2018 and titled “TFT FINGERPRINT SENSOR,” which is incorporated hereinby reference in its entirety.

TECHNICAL FIELD

The present embodiments relate generally to touch sensors, andspecifically to a gate line driver for a fingerprint sensor.

BACKGROUND

Many devices (such as smartphones, tablets, or other personal or mobilecomputing devices) include a fingerprint sensor. The fingerprint sensormay be separate from or integrated into a display panel. A fingerprintsensor typically includes an array of sensor or sensing elementsarranged in rows and columns. Each column of sensing elements is coupledto a respective gate line, and each row of sensing elements is coupledto a respective read-out line. Each gate line (coupling a column ofsensing elements) is coupled to a gate driver, and each read-out line(coupling a row of sensing elements) is coupled to a read-out circuit.

In conventional gate driver implementations, the gate driver is aserial-in serial-out (SISO) shift register, and each flip-flop of theshift register is configured to drive a corresponding column of sensingelements. The gate driver sequentially drives columns of sensingelements from a first column to a last column of the array of sensingelements. A driven column of sensing elements provides voltagesindicating whether a touch exists at the location of the sensing regioncorresponding to each sensing element of the column. The sensingelements for the driven column provide the voltages to the read-outcircuit via the read-out lines. In this manner, the fingerprint sensorsweeps through the entire sensing region in attempting to capture afingerprint. As a result, the time required for scanning is related tothe size of the sensing region for the fingerprint sensor.

The size of the sensing region for fingerprint sensors continues togrow. For example, with fingerprint sensors integrated into displaypanels for devices, a user may be unsure where the fingerprint sensingregion is located on the display. Therefore, device manufacturers maydesire the fingerprint sensor's sensing region to cover a large area ofthe display (e.g., the bottom 25 percent of a smartphone display).Additionally, fingerprint sensors with large sensing regions may becapable of multiple finger scanning (such as for dual-fingerauthentication). However, increased areas to scan increase the timeneeded for scanning. Additionally, the scan images are larger, whichrequire more storage and processing resources than smaller scan images.As a result, increased latency negatively impacts a user's experience.

SUMMARY

This Summary is provided to introduce in a simplified form a selectionof concepts that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tolimit the scope of the claimed subject matter.

An example gate driver for an array of sensing pixels is disclosed. Thegate driver includes a first flip-flop including a first data input anda first data output. The first data output is coupled to a first groupof sensing pixels of the array. The gate driver also includes a secondflip-flop including a second data input and a second data output. Thesecond data output is coupled to a second group of sensing pixels of thearray. The gate driver further includes a first insertion circuitconfigured to receive a first start signal and to cause, based on thefirst start signal, the second flip-flop to drive the second group ofsensing pixels without the first flip-flop driving the first group ofsensing pixels for a scan of the array.

An example sensor is also described. The sensor includes an array ofsensing pixels configured to sense a touch for a sensing region of thesensor and a gate driver configured to drive a portion of the array ofsensing pixels in performing a scan by the sensor. The gate driverincludes a first flip-flop including a first data input and a first dataoutput. The first data output is coupled to a first group of sensingpixels of the array. The gate driver also includes a second flip-flopincluding a second data input and a second data output. The second dataoutput is coupled to a second group of sensing pixels of the array. Thegate driver further includes a first insertion circuit configured toreceive a first start signal and to cause, based on the first startsignal, the second flip-flop to drive the second group of sensing pixelswithout the first flip-flop driving the first group of sensing pixelsfor a scan of the array. The sensor also includes a controllerconfigured to control the gate driver to drive the portion of the arrayin performing the scan.

An example method of operating a gate driver for an array of sensingpixels is disclosed. The method includes determining a portion of thearray of sensing pixels corresponding to one or more touches in asensing region of a sensor, driving the sensing pixels of the array inthe portion for a scan by the sensor, and preventing sensing pixels ofthe array outside the portion from being driven.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments are illustrated by way of example and are notintended to be limited by the figures of the accompanying drawings.

FIG. 1 illustrates a block diagram of an example device for which thepresent embodiments may be implemented.

FIG. 2 illustrates an optical pixel array in an optical fingerprintsensor.

FIG. 3 illustrates an optical pixel.

FIG. 4 illustrates a block diagram of a fingerprint sensor.

FIG. 5 illustrates a block diagram of a gate driver.

FIG. 6 is a timing diagram of the gate driver in FIG. 5.

FIG. 7 illustrates a portion of the gate driver in FIG. 5 including aninsertion circuit for beginning scanning.

FIG. 8A illustrates a first example implementation of the insertioncircuit in FIG. 7.

FIG. 8B illustrates a second example implementation of the insertioncircuit in FIG. 7.

FIG. 9 illustrates a portion of the gate driver in FIG. 5 including aninsertion circuit for beginning and stopping scanning.

FIG. 10A illustrates a first example implementation of the circuit inFIG. 9.

FIG. 10B illustrates a second example implementation of the circuit inFIG. 9.

FIG. 11 illustrates an example sensing region of a fingerprint sensor.

FIG. 12 illustrates the example sensing region in FIG. 11 with twofinger touches.

FIG. 13 is an illustrative flow chart for performing a fingerprint scan,in accordance with some implementations.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forthsuch as examples of specific components, circuits, and processes toprovide a thorough understanding of the present disclosure. The term“coupled” as used herein means connected directly to or connectedthrough one or more intervening components or circuits. Also, in thefollowing description and for purposes of explanation, specificnomenclature is set forth to provide a thorough understanding of theaspects of the disclosure. However, it will be apparent to one skilledin the art that these specific details may not be required to practicethe example embodiments. In other instances, well-known circuits anddevices are shown in block diagram form to avoid obscuring the presentdisclosure. Some portions of the detailed descriptions which follow arepresented in terms of procedures, logic blocks, processing and othersymbolic representations of operations on data bits within a computermemory. The interconnection between circuit elements or software blocksmay be shown as buses or as single signal lines. Each of the buses mayalternatively be a single signal line, and each of the single signallines may alternatively be buses, and a single line or bus may representany one or more of a myriad of physical or logical mechanisms forcommunication between components.

Unless specifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present application,discussions utilizing the terms such as “accessing,” “receiving,”“sending,” “using,” “selecting,” “determining,” “normalizing,”“multiplying,” “averaging,” “monitoring,” “comparing,” “applying,”“updating,” “measuring,” “deriving” or the like, refer to the actionsand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a non-transitory computer-readable storagemedium comprising instructions that, when executed, performs one or moreof the methods described above. The non-transitory computer-readablestorage medium may form part of a computer program product, which mayinclude packaging materials.

The non-transitory processor-readable storage medium may comprise randomaccess memory (RAM) such as synchronous dynamic random access memory(SDRAM), read only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),FLASH memory, other known storage media, and the like. The techniquesadditionally, or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that can beaccessed, read, and/or executed by a computer or other processor.

The various illustrative logical blocks, modules, circuits andinstructions described in connection with the embodiments disclosedherein may be executed by one or more processors. The term “processor,”as used herein may refer to any general purpose processor, conventionalprocessor, controller, microcontroller, and/or state machine capable ofexecuting scripts or instructions of one or more software programsstored in memory.

Turning now to the figures, FIG. 1 is a block diagram of an exampledevice 100, in accordance with some embodiments. The input device 100may be configured to provide input to an electronic system (not shown).As used in this document, the term “electronic system” (or “electronicdevice”) broadly refers to any system capable of electronicallyprocessing information. Some non-limiting examples of electronic systemsor devices include computing systems, such as personal computers of allsizes and shapes (e.g., desktop computers, laptop computers, and netbookcomputers), tablets, smartphones, web browsers, e-book readers, andpersonal digital assistants (PDAs). Additional example computing systemsinclude composite input devices, such as physical keyboards that includedevice 100 and separate joysticks or key switches. Further examplecomputing systems include peripherals such as data input devices(including remote controls and mice), and data output devices (includingdisplay screens and printers). Other examples include remote terminals,kiosks, and video game machines (e.g., video game consoles, portablegaming devices, and the like). Other examples include communicationdevices (including cellular phones, such as smartphones), and mediadevices (including recorders, editors, and players such as televisions,set-top boxes, music players, digital photo frames, and digitalcameras). Additionally, the electronic system could be a host or a slaveto the device.

The device 100 may be implemented as a physical part of the electronicsystem, or may be physically separate from the electronic system. Asappropriate, the device 100 may communicate with parts of the electronicsystem using, e.g., buses, networks, and other wired or wirelessinterconnections. Example technologies may include Inter-IntegratedCircuit (I²C), Serial Peripheral Interface (SPI), PS/2, Universal Serialbus (USB), Bluetooth®, Infrared Data Association (IrDA), and variousradio frequency (RF) communication protocols defined by the IEEE 502.11standard.

The device 100 includes a processing system 110 and a display 130. Thedisplay 130 may be any type of dynamic display capable of displaying avisual interface to a user, and may include any type of light emittingdiode (LED), organic LED (OLED), cathode ray tube (CRT), liquid crystaldisplay (LCD), plasma, electroluminescence (EL), or other displaytechnology. For example, the display 130 may include an array of pixelelements (e.g., liquid crystal capacitors) coupled to a display gatedriver and a display source driver (not shown for simplicity). Each rowof pixel elements may be coupled to the display gate driver via arespective gate line. Each column of pixel elements may be coupled tothe display source driver via a respective source line (or data line).The source driver may be configured to drive pixel data, via the sourcelines, onto the pixel elements of the array. The gate driver may beconfigured to select a particular row of pixel elements to receive thepixel data, for example, by driving the gate line coupled to theselected row. In some aspects, the display 130 may be updated bysuccessively “scanning” the rows of pixel elements (e.g., one row at atime), until each row of pixel elements has been updated.

In some implementations, the device 100 may include or correspond to oneor more position sensor devices. For example, the device 100 may includeor be associated with a fingerprint sensor and proximity sensorconfigured to sense input provided by one or more input objects 140 in asensing region 120. Example input objects 140 for interacting with theinput device 100 include fingers and styli, as shown in FIG. 1. Afingerprint sensor may be a swipe sensor, where a fingerprint image isreconstructed from a series of scans as the user moves their finger overthe sensor, or a placement sensor, where a sufficient area of thefingerprint can be captured from a single scan as the user holds afinger at a fixed location in the sensing region 120.

Sensing region 120 may encompass any space above, around, in and/or nearthe device 100 (e.g., near at least a portion of the display 130) inwhich the device 100 is able to detect user input (e.g., user inputprovided by one or more input objects 140). The sizes, shapes, andlocations of particular sensing regions may vary widely from embodimentto embodiment. In some embodiments, the sensing region 120 extends froma surface of the device 100 in one or more directions into space untilsignal-to-noise ratios prevent sufficiently accurate object detection.The distance to which this sensing region 120 extends in a particulardirection, in various embodiments, may be on the order of less than amillimeter, millimeters, centimeters, or more, and may varysignificantly with the type of sensing technology used and the accuracydesired. Thus, some embodiments sense input that comprises no contactwith any surfaces of the device 100, contact with an input surface (e.g.a touch surface or display) of the device 100, contact with an inputsurface of the device 100 coupled with some amount of applied force orpressure, and/or a combination thereof. In various embodiments, inputsurfaces may be provided by surfaces of casings within which the sensorelectrodes reside, by face sheets applied over the sensor electrodes orany casings, etc. In some embodiments, the sensing region 120 has arectangular shape when projected onto an input surface of the inputdevice 100. In some other embodiments, the sensing region 120 has acircular shape that conforms to the shape of a fingertip. However, thesensing region 120 may have any suitable shape and dimensions. While thesensing region 120 is illustrated as overlapping at least a portion ofan active area of a display 130, the sensing region 120 may be at anysuitable location of the device 100 (e.g., to the side of the display130, on a surface of the device 100 on which the display 130 is notdisposed, etc.). In some other implementations, the device 100 may notinclude a display 130 but include a fingerprint sensor and proximitysensor (e.g., a touchpad).

For sensing, the device 100 may include substantially transparent sensorelectrodes overlaying the display screen and provide a touch screeninterface for the associated electronic system. As another example, thedevice 100 may comprise photosensors in or under the display screen andprovide an optical sensing interface for the associated electronicsystem. The display screen may be any type of dynamic display capable ofdisplaying a visual interface to a user, and may include any type oflight emitting diode (LED), organic LED (OLED), cathode ray tube (CRT),liquid crystal display (LCD), plasma, electroluminescence (EL), or otherdisplay technology. Touch sensors (e.g., the proximity sensor andfingerprint sensor) and the display screen may share physical elements.For example, some embodiments may utilize some of the same electricalcomponents for displaying and sensing.

In some capacitive implementations for input, voltage or current isapplied to create an electric field. Nearby input objects cause changesin the electric field, and produce detectable changes in capacitivecoupling that may be detected as changes in voltage, current, or thelike. Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensing elements to create electricfields. In some capacitive implementations, separate sensing elementsmay be ohmically shorted together to form larger sensor electrodes. Somecapacitive implementations utilize resistive sheets, which may beuniformly resistive.

Some capacitive implementations utilize “self capacitance” (or “absolutecapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes and an input object. An input objectnear the sensor electrodes alters the electric field near the sensorelectrodes, thus changing the measured capacitive coupling. In someexamples, an absolute capacitance sensing method operates by modulatingsensor electrodes with respect to a reference voltage (e.g., systemground), and by detecting the capacitive coupling between the sensorelectrodes and input objects.

Some capacitive implementations utilize “mutual capacitance” (or“transcapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes. An input object near the sensorelectrodes alters the electric field between the sensor electrodes, thuschanging the measured capacitive coupling. In some examples, atranscapacitive sensing method operates by detecting the capacitivecoupling between one or more transmitter sensor electrodes (also“transmitter electrodes” or “transmitters”) and one or more receiversensor electrodes (also “receiver electrodes” or “receivers”).Transmitter sensor electrodes may be modulated relative to a referencevoltage (e.g., system ground) to transmit transmitter signals. Receiversensor electrodes may be held substantially constant relative to thereference voltage to facilitate receipt of resulting signals. Aresulting signal may comprise effect(s) corresponding to one or moretransmitter signals, and/or to one or more sources of environmentalinterference (e.g., other electromagnetic signals). Sensor electrodesmay be dedicated transmitters or receivers, or may be configured to bothtransmit and receive.

In some optical implementations for input, one or more optical detectorelements (or “sensing elements” or “sensing pixels”) are included forimaging an input object or detecting user input. The sensing pixelsdetect light from the sensing region 120. In various embodiments, thedetected light may be reflected from input objects in the sensingregion, emitted by input objects in the sensing region, transmittedthrough input objects in the sensing region, or some combinationthereof. Example sensing pixels include photodiodes, phototransistors, aportion of a CMOS image sensor arrays, a portion of a CCD arrays, and/orany other sensor components capable of detecting wavelengths of light inthe visible, infrared, and/or the ultraviolet spectrum. Some opticalimplementations utilize a light source (e.g., one or more LEDs) toprovide illumination to the sensing region. Light reflected or scatteredfrom the sensing region in the illumination wavelength(s) can bedetected to determine input information corresponding to the inputobject.

In some other implementations, the device 100 may utilize other varioussensing technologies to detect user input. Other example sensingtechnologies may include elastive, resistive, inductive, magnetic,acoustic, and ultrasonic sensing technologies. The devices 100 and 100Amay include additional input components that are operated by theprocessing system 110 or by some other processing system. Theseadditional input components may provide redundant functionality forinput in the sensing region 120, or some other functionality.

In FIG. 1, a processing system 110 is shown as part of the device 100.The processing system 110 may be configured to operate the hardware ofthe device 100 to detect input in the sensing region 120. In someembodiments, the processing system 110 may be implemented as a set ofmodules that are implemented in firmware, software, or a combinationthereof. Example modules include hardware operation modules foroperating hardware such as sensor electrodes and display screens; dataprocessing modules for processing data such as sensor signals andpositional information; and reporting modules for reporting information.In some embodiments, the processing system 110 may include sensoroperation modules configured to operate sensing elements to detect userinput in the sensing region 120; identification modules configured toidentify gestures such as mode changing gestures; and mode changingmodules for changing operation modes of the device 100and/or theelectronic system.

The processing system 110 may comprise parts of or all of one or moreintegrated circuits (ICs) and/or other circuitry components. Forexample, a processing system for a sensor may comprise transmittercircuitry configured to transmit signals with transmitter sensorelectrodes and/or receiver circuitry configured to receive signals withreceiver sensor electrodes.

In some implementations, the processing system 110 may includeelectronically-readable instructions, such as firmware and/or software.In some implementations, components of the processing system 110 arelocated together, such as near sensing element(s) of the device 100. Insome other implementations, components of processing system 110 arephysically separate from the sensing element(s). For example, the device100 may be a peripheral coupled to a desktop computer, and theprocessing system 110 may comprise software configured to run on acentral processing unit of the desktop computer and one or more ICs(perhaps with associated firmware) separate from the central processingunit. As another example, the device 100 may be physically integrated insmartphones, and the processing system 110 may comprise circuits andfirmware that are part of a processor of the respective smartphone. Theprocessing system 110 may be dedicated to controlling the devices 100and 100A, or the processing system 110 may also perform other functions,such as operating the display 130, driving haptic actuators, etc.

The processing system 110 may respond to a user input (or lack of userinput) in the sensing region 120 by causing one or more actions. Exampleactions include changing operation modes (e.g., unlocking the userdevice or providing access to secure data using a detected fingerprint),as well as graphical user interface (GUI) actions such as cursormovement, selection, menu navigation, and other functions. For example,the processing system 110 may provide information about the input (orlack of input) to some part of the electronic system (e.g., to a centralprocessing system of the electronic system that is separate from theprocessing system), and the part of the electronic system processesinformation received from the processing system 110 to act on the userinput (or lack of user input), such as to facilitate a full range ofactions, including mode changing actions and GUI actions. In someimplementations, the processing system 110 may be configured toconcurrently drive display electrodes to update at least a portion ofthe display 130 and sense user inputs in the sensing region 120.

The processing system 110 may operate the sensing element(s) of thedevice 100 to produce electrical signals indicative of input (or lack ofinput) in the sensing region 120. The processing system 110 may performany appropriate amount of processing on the electrical signals inproducing the information provided to the electronic system. Forexample, the processing system 110 may digitize analog electricalsignals obtained from the sensor electrodes. As another example, theprocessing system 110 may perform filtering or other signalconditioning. As yet another example, the processing system 110 maysubtract or otherwise account for a baseline, such that the informationreflects a difference between the electrical signals and the baseline.As yet further examples, the processing system 110 may determinepositional information, recognize inputs as commands, recognizehandwriting, and so on.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Example “zero-dimensional” positional informationincludes near/far or contact/no contact information. Example“one-dimensional” positional information includes positions along anaxis. Example “two-dimensional” positional information includes motionsin a plane. Example “three-dimensional” positional information includesinstantaneous or average velocities in space. Further examples includeother representations of spatial information. Historical data regardingone or more types of positional information may also be determinedand/or stored, including, for example, historical data that tracksposition, motion, or instantaneous velocity over time.

It should be understood that while many embodiments of the technologyare described in the context of a fully functioning apparatus, themechanisms of the present technology are capable of being distributed asa program product (e.g., software) in a variety of forms. For example,the mechanisms of the present technology may be implemented anddistributed as a software program on information bearing media that arereadable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present technology apply equally regardless of the particular typeof medium used to carry out the distribution. Examples ofnon-transitory, electronically readable media include various discs,memory sticks, memory cards, memory modules, and the like.Electronically readable media may be based on flash, optical, magnetic,holographic, or any other storage technology.

As noted above, the device 100 may use optical sensing technologies tosense a touch. FIGS. 2-3 are regarding example optical sensingtechnology which may be used in a device or computing system to sense atouch in a sensing region of the device or computing system. FIGS. 2-3are described below in reference to the device 100 in FIG. 1 forillustrative purposes. However, the input device 100 is only an exampledevice. Any other suitable devices or computing systems may be used, andthe present disclosure is not limited to the provided examples.

FIG. 2 illustrates an optical pixel array 200 in an optical fingerprintsensor. The optical pixel array 200 includes a plurality of sensingpixels, which may include photodiodes (PDs) 205 arranged into arectangular matrix array which are coupled to data lines 220 using arespective thin-film transistor (TFT) 210. The TFTs 210 include gatesthat are coupled to respective gate lines 215. Each of the PDs 205 isconnected to a data line 220 through a source and drain of theassociated TFT 210. Driving different voltages on the gate lines 215either activates (e.g., opens) or deactivates (e.g., closes) the TFTs210. When activated, the TFTs 210 electrically couple the PDs 205 to thedata lines 220. As described below, the data lines 220 can be used topre-charge the PDs 205 and to measure voltages corresponding to the PDs205 in order to capture a fingerprint for a human finger. Whendeactivated, the PDs 205 are electrically floating—i.e., areelectrically disconnected for the data lines 220. Although not shown,each data line 220 may be coupled to a respective analog front end (AFE)(also called an optical AFE) which can measure charge, voltage, orcurrents corresponding to the PDs 205 to capture a fingerprint.

To use optical sensing to capture a fingerprint, one or more lightsources (not shown in FIG. 2) may be included separate from orintegrated within the optical pixel array 200, which emit light towardsa sensing region where a finger is disposed. The light interacts withthe finger (e.g., is reflected or scattered by the finger) and changesin the optical response due the interaction of the light with the fingerare detected by the PDs 205. For example, the light reflected orscattered by the finger may be detected by the PDs. In one embodiment,the optical pixel array 200 includes gate driver circuitry whichcontrols the voltages on the gate lines 215 in order to activate anddeactivate the TFTs 210. In some embodiments, the gate driver circuitryincludes a shift register which permits the optical fingerprint toraster through the rows. For example, when performing optical sensing,at any given time the device may couple only one row of the PDs 205 tothe data lines 220 while the other rows of PDs 205 are disconnected fromthe data lines 220. The gate driver circuitry can use one of the gatelines 215 to activate all of the TFTs 210 coupled to the gate line 215while driving voltages on the other gate lines 215 which deactivate theTFTs 210 in the remaining rows.

In one embodiment, the optical pixel array 200 connects a selected rowof the PDs 205 to the data lines 220. The optical AFEs coupled to thedata lines 220 pre-charge a capacitance corresponding to the PDs 205 inthe selected row. After pre-charging the PDs 205 in the row, the gateline 215 deactivates the TFTs which disconnects the PDs 205 in the rowfrom the data lines 220. While disconnected, one or more light sourcesemit light which interacts with the finger (if present) and at least aportion of the light is detected by the PDs 205 which changes a leakagecurrent corresponding to the PDs 205 relative to a leakage current whenno (or less) light strikes the PDs 205. The PDs 205 are then reconnectedto the data lines 220 using the selected gate line 215 and the TFTs 210.The optical AFEs coupled to the data lines 220 then measure voltagescorresponding to the PDs in the selected row. By measuring the voltage(or the change in the voltage), the input device can determine ridgesand valleys in the finger in order to capture a fingerprint. However,this is just one example of performing optical sensing. The embodimentsdescribed herein can be used with other techniques for performingoptical sensing to capture a fingerprint.

The optical pixel array 200 includes an area and a pitch suitable forcapturing a fingerprint (e.g., a full or partial fingerprint areasufficient for reliably performing fingerprint authentication). In oneembodiment, the optical pixel array 200 includes an area ranging from 20mm² to 100 mm². In one embodiment, the optical pixel array 200 includesa pitch of photodiodes ranging from 5 microns to 100 microns. Otherdimensions may be suitable for the optical pixel array 200 in someimplementations. Although photodiodes are specifically mentioned, theembodiments herein can apply to other types of photosensors such as aphototransistor.

FIG. 3 illustrates an optical pixel 300. FIG. 3 may be a schematiccross-sectional view of one of the PDs 205 and TFTs 210 illustrated inFIG. 2, and the example in FIG. 3 illustrates the general electricalconnections between the various components in the optical pixel 300. Theparticular spatial arrangement shown in FIG. 4 is an example and otherarrangements are possible. The optical pixel 300 includes a TFTsubstrate 335 on which the TFT 210 (switch) and the PD 205 (photosensor)are disposed. In one embodiment, the TFT substrate 335 is made of glass.FIG. 3 is a simplified schematic to illustrate some functionalcomponents of the optical pixel 300 in a dual optical and capacitivesensor, but it should be understood that the optical pixel 300 caninclude various metal routing layers, insulation layers, andsemiconductor layers disposed over the TFT substrate 335 in variousconfigurations.

In the optical pixel 300, one terminal of the TFT 210 is coupled to adata connector 310 (e.g., data metal) which couples the TFT 210 to oneof the data lines 220 shown in FIG. 2. Another terminal of the TFT 210is coupled to a PD connector 325 which couples the TFT to the PD 205. Agate metal 330 is coupled to one of the gate lines 215 in FIG. 2 andcontrols a gate of the TFT 210 to form a conductive channel in the TFT210. When formed, the conductive channel electrically connects the dataconnector 310 to the PD connector 325 to charge the PD 205 or to measurea voltage corresponding to the PD 205 as described above. In otherwords, the gate metal 330 can activate and deactivate the TFT 210 inorder to selectively couple the data connector 310 to the PD connector325.

In some implementations, the TFT 210 includes at least one doped activesemiconductor layer (e.g., doped silicon) which can be used to form theconductive channel in response to the voltages driven on the gate metal330. In one example, the TFT 210 includes amorphous silicon. Because theactive structures in the TFT 210 can be affected by light, the opticalpixel 300 may include a light shield 305 which blocks some or all of thelight emitted when performing optical sensing (as well as ambient light)from striking the TFT 210. The light shield 305 may be formed of anopaque metal layer.

As shown, the bottom surface of the PD 205 (e.g., a first surface) iscoupled to the PD connector 325 while a top, opposite surface of the PD205 (e.g., a second surface) is coupled to a capacitive sensor layer320. The capacitive sensor layer 320 may include one or more capacitivesensor electrodes. In one example, the capacitive sensor layer 320includes a single capacitive sensor electrode (e.g., to detect apresence of a finger) which is connected to all of the PDs 205 in theoptical pixel array. In another example, the capacitive sensor layer 320includes a plurality of capacitive sensor electrodes arranged in apattern having a lower resolution and/or lower sensor pitch betweenelectrodes than the optical pixel array. One of the capacitive sensorelectrodes may be electrically connected to multiple ones of the PDs 205in the pixel array. In some implementations, the capacitive sensor layer320 includes a plurality of capacitive sensor electrodes arranged in apattern having the same resolution or sensor pitch between electrodes asthe optical pixel array. Each of the capacitive sensor electrodes may beelectrically connected to a respective one of the PDs 205 in the opticalpixel array. When performing optical sensing, the capacitive sensorlayer 320 is coupled to a reference or bias voltage (referred to hereinas Vcom), and the capacitive sensor electrodes, which are electricallycoupled to the PD 205, are held at a constant, unmodulated voltage. Forcapacitive sensing, the sensor electrodes in the capacitive sensor layer320 may be driven with a capacitive sensing signal (e.g., an AC signal)in order to detect the presence or movement of an input object in thesensing region.

In some implementations, the sensing region 120 (FIG. 1) is the areaabove a top surface of the device (which may be a top surface of thepassivation layer 315 or a top surface of an additional cover layerdisposed above the passivation layer 315, such as a cover glass). Byperforming capacitive sensing using the capacitive sensor layer 320, theinput device can determine when an input object is proximate to theoptical pixel 300—i.e., when the input object is in the sensing region.In some implementations, the capacitive sensor layer 320 may beconsidered part of or included in the proximity sensor, while opticalsensing components (including the PD 205) may be considered part of thefingerprint sensor.

An input object may not need to contact the input surface in order to bedetected by the capacitive sensor layer 320, but can be hovering overthe input surface. In some implementations, the input object is detectedby the capacitive sensor layer 320 when it is in contact with the inputsurface over the PD 205. The term “touch” may refer to contact or closeproximity to an input surface (such as “hovering”).

The passivation layer 315 may be a dielectric material. Moreover, thepassivation layer 315 and the capacitive sensor layer 320 may be formedfrom optically transparent material such that light from the sensingregion can pass through these layers in order to reach the PD 205. Inone embodiment, the capacitive sensor layer 320 is formed of atransparent conductor, such as indium tin oxide (ITO), which isoptically transparent but also is conductive. In that way, thecapacitive sensor layer 320 can be driven to Vcom during optical sensing(e.g., for fingerprint scanning) and can be driven with a capacitivesensing signal when the fingerprint performs capacitive sensing. In oneembodiment, the capacitive sensor layer 320 may also be referred to asan ITO bias layer.

Conventional fingerprint sensors scan an entire sensing region for afingerprint scan. For example, each column of an array of sensing pixelsis driven to provide sensing values (such as a current indicating apresence/ridge or lack of presence/valley of an object/finger at thecorresponding location) for each respective pixel. A fingerprint imagemay then be constructed from the sensing values.

FIG. 4 illustrates a block diagram of a fingerprint sensor 400. In someimplementations, the fingerprint sensor 400 may be based on opticalsensing and include components as illustrated in FIGS. 2 and 3. Theexample fingerprint sensor 400 includes a TFT sensor 402 coupled tosilicon 408. The silicon 408 includes other components of the computingsystem. For example, a controller 414 may be implemented in the silicon408 and configured to provide control signals to the gate driver 404 ofthe TFT sensor 402. The silicon 408 also includes a read-out circuit 410configured to receive the sensing values provided by the TFT sensor 402.The sensing values may be used to construct a fingerprint image orotherwise be used to identify one or more fingerprints.

The TFT sensor 402 includes a gate driver 404 and an array of sensingpixels 406 coupled to the gate driver 404 via gate lines 412. The arrayis also coupled to the read-out circuit 410 via read-out lines 416. Theexample array includes rows 0-Y and columns 0-X of sensing pixels 406,with each sensing pixel associated with a specific row and column. Forexample, a sensing pixel 406 of a specific column of the array iscoupled to the gate driver 404 via the corresponding gate line 412. Thegate driver 404 is configured to drive the sensing pixel 406 by drivingthe corresponding gate line 412. The sensing pixel 406 is also coupledto the read-out circuit via the corresponding read-out line 416. Theread-out circuit 410 is configured to receive the signal provided by thesensing pixel 406 when the sensing pixel 406 is driven by the gatedriver 404.

The number of columns and rows of the array corresponds to the size ofthe sensing region of the fingerprint sensor. For example, a largersensing region corresponds to an increase in the number of columnsand/or rows of sensing pixels 406. If the number of columns increases,the number of gate lines 412 increases, and the logic of the gate driver404 increases for driving the increased number of gate lines 412.

FIG. 5 illustrates a block diagram of a gate driver 500. The gate driver500 may be a SISO shift register coupled to the gate lines of the arrayand configured to sequentially drive the gate lines. The gate driver 500includes a plurality of flip-flops 502-0 through 502-X that aresequentially coupled, a start voltage (STV) line 504 coupled to thefirst flip-flop 502-0, a clock (CLK) line 506 coupled to alternatingflip-flops, an inverse clock (CLKB) line 508 coupled to the otherflip-flops, and a RESET line 510 coupled to each of the flip-flops. Asignal on the STV line 504 may be provided by a controller (such ascontroller 414 in FIG. 4) to begin a fingerprint scan, with the clockand inverse clock signals (on lines CLK 506 and CLKB 508, respectively)controlling the timing of sequentially driving the corresponding gatelines. A flip-flop 502-0 through 502-X may drive a corresponding gateline by providing a high signal (a “1”) on its output G0—GX,respectively. The RESET line 510 may be used to reset the gate driver500. For example, when a fingerprint scan is complete (or if afingerprint scan is to be terminated before completion), a controller(such as controller 414) may drive the RESET line 510 to 1 to reset theshift register (causing the outputs G0-GX to return to a low signal (a“0”)).

FIG. 6 is a timing diagram 600 of the operation of the gate driver 500in FIG. 5. With the clock signal (CLK) and inverse clock signal (CLKB)provided to the flip-flops, the STV signal of 1 provided at time t₀ tothe flip-flop 502-0 may initialize the gate driver 500. As a result, theflip-flop 502-0 output G0 is driven to 1 at time t₁. Output G0 equal to1 drives the first column (e.g., column 0) of the array of sensingpixels to provide sensing values to the read-out circuit.

With a 1 provided to the next flip-flop 502-1 at time t₁, output G1 fromthe flip-flop 502-1 is driven to 1; at time t₂. In this manner, theoutputs G0 through GX are driven to 1 in sequence, causing the columnsof the array of sensing pixels to be driven sequentially (e.g., G2driven to 1 at t₃, G(X−1) driven to 1 at tx, and GX driven to 1 att_(x+1)). The reset signal may be provided after t_(x+1) when scanningof the sensing region is complete (not shown).

As sensing regions of fingerprint sensors increase in size, a gatedriver to sequentially drive each column of sensing elements or pixelsmay cause an increase in the time to perform a fingerprint scan. In someimplementations, a fingerprint sensor may be configured to scan only aportion of the sensing region. For example, the fingerprint sensor mayinclude a gate driver configured to drive only a portion of the sensingpixels for a fingerprint scan. In this manner, the fingerprint sensormay reduce the time for performing a fingerprint scan.

FIG. 7 illustrates a portion 700 of the gate driver 500 in FIG. 5,including insertion circuit 702 for beginning scanning by driving outputGn to 1.As shown, the data input D of the flip-flop 502-n is coupled toinsertion circuit 702, which is configured to control whether scanningshould begin at column n of the array of sensing pixels. In someimplementations, a controller (such as controller 414) that determinesthe scan should begin at column n may drive STVn signal 704 to 1.Insertion circuit 702 is configured to initialize the gate driver 500 byproviding the 1 to the data input D of the flip-flop 502-n. If thecontroller determines that the scan is to begin at a column beforecolumn n of the array, a different STV signal may be driven to 1 (suchas on STV line 504 to begin scanning with column 0 of the array or adifferent STV line for a separate insertion circuit). In this manner,output Gn-1 is driven to 1, which is provided to the insertion circuit702. Insertion circuit 702 may be further configured to provide the 1 tothe data input D of the flip-flop 502-n to continue the fingerprintscan.

In some example implementations, each flip-flop of the gate driver maybe coupled to an insertion circuit corresponding to the respectiveflip-flop. In this manner, the fingerprint sensor may begin afingerprint scan at any column of the array. In some other exampleimplementations, a subset of the flip-flops may be coupled to aninsertion circuit corresponding to the respective flip-flop. Forexample, flip-flops spaced a predetermined number of flip-flops from oneanother may be coupled to a corresponding insertion circuit, and theremaining flip-flops may be as configured in FIG. 5 (without insertioncircuit 702). The fingerprint scan may therefore begin at one of thecolumns driven by one of the flip-flops spaced the predetermined numberof flip-flops apart.

FIGS. 8A and 8B illustrate example implementations of the insertioncircuit 702 in FIG. 7. As noted above, the insertion circuit 702 may beconfigured to provide a 1 to the flip-flop 502-n when either the STVnsignal 704 is 1 or the output Gn-1 from the flip-flop 502-(n−1) is 1. InFIG. 8A, the insertion circuit 702 includes an OR gate 802 for OR'ingthe STVn signal 704 and the output Gn-1. In FIG. 8B, the insertioncircuit 702 includes a NAND gate 804. In the example, the inputs to theNAND gate 804 are the inverse of STVn signal 704 (STVnB 806) and theinverse of the output Gn-1 (Gn-1 B 808). In some implementations, theSTVn signal 704 may be inverted before being provided to the NAND gate804. For Gn-1 B 808, the flip-flop 502-(n−1) may include an inverseoutput (e.g., Oft not shown) that may be coupled to the NAND gate 804.Alternatively, the output Gn-1 may be inverted before being provided tothe NAND gate 804.

As noted above, the controller 414 may use the RESET line 510 toterminate a fingerprint scan before one or more columns of the array ofsensing pixels are driven. In this manner, the fingerprint sensor mayscan only a portion of the sensing region for a fingerprint scan. Forexample, a fingerprint scan may begin after a first column of the array(by using insertion circuit 702 to start at column 502 n), and thefingerprint scan may end before a last column of the array (by using theRESET line 510 to end at the column last driven by the gate driver 500).

A fingerprint sensor configured to scan only a portion of the sensingregion may be configured for dual-fingerprint or multi-fingerprintscanning. In some implementations, multiple portions of the sensingregion may be scanned for a fingerprint scan. For example, a gate driver500 may sequentially drive a number (s) of columns of the array (e.g.,corresponding with a first fingerprint), not drive a subsequent number(t) of columns, and drive a subsequent number (t) of columns (e.g.,corresponding with a second fingerprint). Any number of portions andportions of any size of the array may be driven by the gate driver 500.Additionally, a single portion of the array may be driven for scanningmultiple fingerprints, and the present disclosure is not limited to theprovided examples.

FIG. 9 illustrates a portion 900 of the gate driver 500 in FIG. 5including insertion circuit 902 for beginning and stopping scanning. Inaddition or alternative to a RESET line 510 being used, a stop signalSTOPnB 904 may be provided by a controller to stop a scan. The portion900 of the gate driver 500 includes flip-flops 502-(n−1) and 502-n, andinsertion circuit 902 coupled between the output Gn-1 from the flip-flop502-(n−1) and the D input for flip-flop 502-n. Insertion circuit 902 isconfigured to control whether scanning should begin at column n of thearray of sensing pixels. In some implementations, the controller 414that determines the scan should begin at column n may drive STVn signal704 to 1. Insertion circuit 902 is configured to initialize the gatedriver 500 by providing the 1 to the data input D of the flip-flop502-n. If the controller 414 determines that the scan is to begin at acolumn before column n of the array, a different STV signal may bedriven to 1. In this manner, output Gn-1 is driven to 1, which isprovided to the insertion circuit 902. Insertion circuit 902 may befurther configured to provide the 1 to the data input D of the flip-flop502-n to continue the fingerprint scan.

Insertion circuit 902 is also configured to control whether an existingscan should end at column n-1 of the array of sensing pixels. In someimplementations, when the STOPnB signal 904 is 1, insertion circuit 902operates similar to insertion circuit 702 in FIG. 7. When the STOPnBsignal 904 is 0, the output of insertion circuit 902 is driven to 0, andthe gate driver 500 is prevented from driving column n of the array ofsensing pixels. In this manner, the controller 414 may drive the STOPnBsignal 904 to 0 to cause the gate driver 500 to terminate scanning afterdriving column n−1 of the array of sensing pixels.

FIGS. 10A and 10B illustrate example implementations of the insertioncircuit 902 in FIG. 9. As noted above, the insertion circuit 902 may beconfigured to provide a 1 to the flip-flop 502-n when either the STVnsignal 704 is 1 or the output Gn-1 from the flip-flop 502-(n−1) is 1when STOPnB signal 904 remains 1. When STOPnB signal 904 is 0, theinsertion circuit 902 may provide a 0 to the flip-flop 502-nirrespective of STVn signal 704 and output Gn-1. In FIG. 10A, theinsertion circuit 902 includes the OR gate 802 (FIG. 8A) and an AND gate1004. The output 1002 of the OR gate 802 is an input to the AND gate1004, with STOPnB signal 904 being the other input to the AND gate 1004.In this manner, the insertion circuit 902 outputs a 1 when STOPnB signal904 is 1 and either STVn signal 704 or output Gn-1 is 1. In FIG. 10B,the insertion circuit 902 includes the NAND gate 804 (FIG. 8B) and a NORgate 1006. The output 1010 of the NAND gate 804 is an input to the NORgate 1006. Another input to the NOR gate 1006 is an inverse signal ofSTOPnB signal 904 (STOPn signal 1008). In this manner, the insertioncircuit 902 outputs a 1 when STOPn signal 1008 is 0 and either STVnsignal 704 or output Gn-1 is 1. In some implementations, the STOPnBsignal 904 may be inverted before being provided to the NOR gate 1006.In some other implementations, a controller may provide STOPn signal1008 without providing STOPnB signal 904 to the insertion circuit 902.

In some implementations, the insertion circuit for starting a scan (andin some implementations, for stopping a scan) may exist for only aportion of the flip-flops of the gate driver 500. A number of flip-flopsbetween such flip-flops may not include a corresponding insertioncircuit for starting and/or stopping scanning. In one example, theinsertion circuit may be disposed such that the flip-flops able to startand stop the scan are spaced a number of flip-flops apart. In someimplementations, the number may be variable. For example, flip-flopswith an insertion circuit may be more prevalent towards the middle of asensing region (e.g., where a finger touch is more likely to occur). Insome other implementations, the number may be constant. For example,insertion circuits may be uniformly disposed for the sensing region ofthe fingerprint sensor.

FIG. 11 illustrates an example sensing region 1102 of a fingerprintsensor. The sensing region includes an array of sensing pixels, whichmay be coupled to the gate driver 1104. The gate driver 1104 in theillustrated example includes a first subset of flip-flops 1112 includingor coupled to an insertion circuit and a second subset of flip-flops1114 not including or coupled to an insertion circuit. The fingerprintsensor may begin scanning of the sensing region 1102 at a column ofsensing pixels coupled to one of the first subset of flip-flops.

In one example for scanning a fingerprint for a finger touch 1110 in thesensing region 1102, the fingerprint sensor may scan the region 1108,which is only a portion of the entire scanning region 1102. Thecontroller 414 may determine to begin scanning at the column of sensingpixels associated with flip-flop 1116 (which includes an insertioncircuit). In this manner, the columns of sensing pixels associated withthe first flip-flop through the flip-flop before flip-flop 1116 are notdriven, and the associated portion of the sensing region 1102 is notscanned. After driving the column of sensing pixels associated withflip-flop 1116, the gate driver 1104 may continue to drive subsequentcolumns of the sensing pixels.

In some implementations, the scan may continue until the remainingcolumns of the sensing region 1102 are driven. In some otherimplementations, the controller 414 may also determine to terminate thescan at a column subsequent to the finger touch 1110. For example, thecontroller 414 may determine to prevent the gate driver 1104 fromdriving the column of sensing pixels associated with flip-flop 1118. Ifthe insertion circuit for flip-flop 1118 is configured to also stopscans, the controller 414 may provide a signal to the insertion circuitfor flip-flop 1118 to stop the scan. In this manner, the column ofsensing pixels coupled to the flip-flop 1118 is not driven.Additionally, or alternatively, the controller 414 may determine to stopthe scan at any column of sensing pixels (including columns associatedwith the second set of flip-flops 1114) through timing the reset signalto coincide with which column of sensing pixels should not be driven bythe gate driver 1104.

While FIG. 11 illustrates one finger touch 1110, the fingerprint sensormay be configured to scan multiple fingerprints for concurrent fingertouches in the sensing region 1102. For example, the fingerprint sensormay be configured for dual-fingerprint authentication where a userplaces two fingers concurrently on the fingerprint sensor in order to beidentified by the computing system (such as the user's smartphone orpersonal computing device). The controller 414 may determine multipleplaces in the sensing region 1102 to start and stop scanning so thatmultiple regions similar to region 1108 may be scanned. The regions maybe scanned in any order through the use of insertion circuits fordifferent flip-flops of the gate driver 1104. In one example, theregions may be scanned in the order they appear in the sensing region1102 in regards to the sequence of flip-flops for the gate driver 1104.

FIG. 12 illustrates the example sensing region 1102 of a fingerprintsensor with two finger touches 1202 and 1204. In one example forscanning multiple fingerprints for finger touches 1202 and 1204 in thesensing region 1102, the fingerprint sensor may scan the region 1206(for finger touch 1202) and the region 1208 (for finger touch 1204). Forregion 1206, the controller 414 may determine to begin scanning at thecolumn of sensing pixels associated with flip-flop 1210 (which includesan insertion circuit). In this manner, the columns of sensing pixelsassociated with the first flip-flop through the flip-flop beforeflip-flop 1210 are not driven, and the associated portion of the sensingregion 1102 is not scanned. After driving the column of sensing pixelsassociated with flip-flop 1210, the gate driver may continue to drivesubsequent columns of the sensing pixels. In the example, the controller414 may determine to prevent the gate driver 1404 from driving thecolumn of sensing pixels associated with flip-flop 1212. If theinsertion circuit for flip-flop 1212 is configured to also stop scans,the controller 414 may provide a signal to the insertion circuit forflip-flop 1212 to stop the scan. In this manner, the column of sensingpixels coupled to the flip-flop 1212 is not driven. Additionally, oralternatively, the controller 414 may determine to stop the scan throughtiming the reset signal.

The fingerprint sensor may scan region 1208 for a second fingerprintbefore or after scanning region 1206 for a first fingerprint. For region1208, the controller 414 may determine to begin scanning at the columnof sensing pixels associated with flip-flop 1214 (which includes aninsertion circuit), and the controller 414 may determine to prevent thegate driver 1104 from driving the column of sensing pixels associatedwith flip-flop 1216. While scanning for two fingerprints areillustrated, the fingerprint sensor may be configured to scan for anysuitable number of fingerprints.

The controller to control the fingerprint sensor (such as controller414) may be included in or external to the fingerprint sensor. Thecontroller 414 may be included in the processing system 110 as aprocessor executing software, dedicated circuitry, or otherimplementations of a controller. In determining which portions of thesensing region 1102 are to be scanned, the controller 414 may determinethe approximate location(s) of the finger touch(es) in the sensingregion 1102. In some example implementations of a computing system, aproximity sensor is configured to determine an approximate location of atouch in a sensing region of the fingerprint sensor. The proximitysensor may then provide the determined location to the controller 414for the controller 414 to determine which portions of the sensing regionare to be scanned. For example, the capacitive sensor layers of aproximity sensor may be used to sense objects at one or more locationsin the sensing region 1102 to be scanned. The controller 414 may thencontrol an optical scanning of those one or more locations in thesensing region 1102 to perform a fingerprint scan.

FIG. 13 is an illustrative flow chart of an example process 1300 forperforming a fingerprint scan. Beginning at 1302, a computing system maydetermine a portion of the fingerprint sensor's sensing region to scan.In some example implementations, the controller 414 may receive from aproximity sensor an indication of a location of a finger touch in thesensing region (1304). The controller 414 may then determine, based onthe location of the finger touch, a first flip-flop of the gate driverto drive to begin scanning the portion of the sensing region (1306). Insome example implementations, the controller 414 may also determine,based on the location of the finger touch, a second flip-flop(subsequent to the first flip-flop) of the gate driver to prevent beingdriven to end scanning (1308). In some other example implementations, asecond flip-flop is not determined, as scanning may be allowed tocontinue until the remainder of the scanning region associated withflip-flops subsequent to the first flip-flop of the gate driver isscanned.

The controller 414 may then control the fingerprint sensor to scan thedetermined portion of the fingerprint sensor (1310). If the firstflip-flop to begin scanning is determined (1306), the controller 414 maydrive the first flip-flop of the gate driver to begin scanning theportion of the sensing region (1312). For example, the controller 414may provide a STVn signal 704 of 1 to insertion circuit 702 or 902 forthe flip-flop 502-n of gate driver 500 if determined to be the firstflip-flop. As a result, the column of sensing pixels coupled to outputGn, and subsequent columns, are driven in sequence for scanning theportion of the sensing region.

If the second flip-flop to end scanning is determined (1308), thecontroller 414 may prevent the second flip-flop of the gate driver frombeing driven to end scanning the portion of the sensing region (1314).In one example, the controller 414 may provide a STOPnB signal 904 of 0to insertion circuit 902 for the flip-flop 502-n of gate driver 500 ifdetermined to be the second flip-flop. As a result, the column ofsensing pixels coupled to output Gn, and subsequent columns, are notdriven, and the associated portion of the scanning region is notscanned. In another example, the controller 414 may provide a RESET 510to all flip-flops of the gate driver 500, thus ending scanning.

Process 1300 may be repeated for multiple portions of the fingerprintsensor's sensing region to capture multiple fingerprints. For example,if the proximity sensor indicates that multiple touches are located inthe sensing region, process 1300 may be performed for each touch in thesensing region.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the aspects disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the disclosure.

The methods, sequences or algorithms described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. An examplestorage medium is coupled to the processor such that the processor canread information from, and write information to, the storage medium. Inthe alternative, the storage medium may be integral to the processor.

In the foregoing specification, embodiments have been described withreference to specific examples thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader scope of the disclosure as set forth in theappended claims. For example, while the provided examples are describedregarding a fingerprint sensor, implementations also apply to otherscanners including a gate driver for sequential scanning of a scanningregion. Additionally, while the sensing region of a scanner is describedas an array with columns and rows, any suitable configuration of thesensing elements may exist (e.g., radial patterns, arcs, diagonals,etc.), and the gate driver may be configured to drive suitable groups ofsensing elements corresponding to their configuration. Further, while“touch” is used in describing sensing in a sensing region, “touch” mayrefer to an object in close proximity to a portion of the sensing region(such as a finger hovering over a fingerprint sensor), and the term“touch” does not require physical contact. Additionally, while the gatedriver is described as being controlled by controller 414, any suitablemeans for controlling the gate driver may be used. For example, the gatedriver may include the controller, or the gate driver may be controllerby means external to the device or computing system including thefingerprint scanner. The specification and drawings are, accordingly, tobe regarded in an illustrative sense rather than a restrictive sense.

What is claimed is:
 1. A gate driver for an array of sensing pixels, thegate driver comprising: a first flip-flop including a first data inputand a first data output, wherein the first data output is coupled to afirst group of sensing pixels of the array; a second flip-flop includinga second data input and a second data output, wherein the second dataoutput is coupled to a second group of sensing pixels of the array; anda first insertion circuit configured to receive a first start signal andto cause, based on the first start signal, the second flip-flop to drivethe second group of sensing pixels without the first flip-flop drivingthe first group of sensing pixels for a scan of the array.
 2. The gatedriver of claim 1, wherein: the first group of sensing pixels is a firstcolumn of sensing pixels in the array; and the second group of sensingpixels is a second column of sensing pixels subsequent to the firstcolumn of sensing pixels in the array.
 3. The gate driver of claim 2,wherein the first insertion circuit includes a logical OR gateconfigured to perform an OR operation on the first start signal and asignal from the first data output from the first flip-flop and providethe result to the second data input of the second flip-flop.
 4. The gatedriver of claim 2, wherein each flip-flop of the gate driver includes aRESET input to receive a reset signal to stop the scan.
 5. The gatedriver of claim 2, wherein the first insertion circuit is furtherconfigured to receive a first stop signal and to prevent, based on thefirst stop signal, the second flip-flop from driving the second columnof sensing pixels after the first flip-flop drives the first column ofsensing pixels.
 6. The gate driver of claim 5, wherein the firstinsertion circuit further includes a logical OR gate and a logical ANDgate, wherein: the logical OR gate is configured to perform an ORoperation on the first start signal and the first data output from thefirst flip-flop and provide the result to the AND gate; and the logicalAND gate is configured to perform an AND operation on the result fromthe OR gate and the first reset signal and provide the result to thesecond data input of the second flip-flop.
 7. The gate driver of claim5, further comprising: a third flip-flop including a third data inputand a third data output, wherein the third data output is coupled to athird column of sensing pixels of the array; a fourth flip-flopincluding a fourth data input and a fourth data output, wherein thefourth data output is coupled to a fourth column of sensing pixels ofthe array; and a second insertion circuit configured to receive a secondstart signal and a second stop signal, the second insertion circuitbeing configured to: cause, based on the second start signal, the fourthflip-flop to drive the fourth column of sensing pixels without the thirdflip-flop driving the third column of sensing pixels; and prevent, basedon the second stop signal, the fourth flip-flop from driving the fourthcolumn of sensing pixels after the third flip-flop drives the thirdcolumn of sensing pixels.
 8. The gate driver of claim 2, furthercomprising: a plurality of additional flip-flops in sequence, whereinthe first flip-flop and the second flip-flop are in the sequence; and aplurality of additional insertion circuitries, wherein an output of eachof the plurality of additional insertion circuitries is coupled to adata input of a corresponding flip-flop of the plurality of additionalflip-flops.
 9. The gate driver of claim 8, wherein the number ofinsertion circuits is less than the number of flip-flops in sequence inthe gate driver.
 10. The gate driver of claim 9, wherein the array ofsensing pixels is included in a fingerprint sensor.
 11. A sensor,comprising: an array of sensing pixels configured to sense a touch for asensing region of the sensor; a gate driver configured to drive aportion of the array of sensing pixels in performing a scan by thesensor, the gate driver including: a first flip-flop including a firstdata input and a first data output, wherein the first data output iscoupled to a first group of sensing pixels of the array; a secondflip-flop including a second data input and a second data output,wherein the second data output is coupled to a second group of sensingpixels of the array; and a first insertion circuit configured to receivea first start signal and to cause, based on the first start signal, thesecond flip-flop to drive the second group of sensing pixels without thefirst flip-flop driving the first group of sensing pixels for a scan ofthe array; and a controller configured to control the gate driver todrive the portion of the array in performing the scan.
 12. The sensor ofclaim 11, wherein: the first group of sensing pixels is a first columnof sensing pixels in the array; and the second group of sensing pixelsis a second column of sensing pixels subsequent to the first column ofsensing pixels in the array.
 13. The sensor of claim 12, wherein thefirst insertion circuit includes a logical OR gate configured to performan OR operation on the first start signal and a signal from the firstdata output from the first flip-flop and provide the result to thesecond data input of the second flip-flop.
 14. The sensor of claim 12,wherein each flip-flop of the gate driver includes a RESET input toreceive a reset signal to stop the scan.
 15. The sensor of claim 12,wherein the first insertion circuit is further configured to receive afirst stop signal and to prevent, based on the first stop signal, thesecond flip-flop from driving the second column of sensing pixels afterthe first flip-flop drives the first column of sensing pixels.
 16. Thesensor of claim 15, wherein the first insertion circuit further includesa logical OR gate and a logical AND gate, wherein: the logical OR gateis configured to perform an OR operation on the first start signal andthe first data output from the first flip-flop and provide the result tothe AND gate; and the logical AND gate is configured to perform an ANDoperation on the result from the OR gate and the first reset signal andprovide the result to the second data input of the second flip-flop. 17.The sensor of claim 15, wherein the gate driver further includes: athird flip-flop including a third data input and a third data output,wherein the third data output is coupled to a third column of sensingpixels of the array; a fourth flip-flop including a fourth data inputand a fourth data output, wherein the fourth data output is coupled to afourth column of sensing pixels of the array; and a second insertioncircuit configured to receive a second start signal and a second stopsignal, the second insertion circuitry being configured to: cause, basedon the second start signal, the fourth flip-flop to drive the fourthcolumn of sensing pixels without the third flip-flop driving the thirdcolumn of sensing pixels; and prevent, based on the second stop signal,the fourth flip-flop from driving the fourth column of sensing pixelsafter the third flip-flop drives the third column of sensing pixels. 18.The sensor of claim 12, wherein the sensor is a fingerprint sensorconfigured to scan multiple concurrent fingerprints during the scan. 19.The scanner of claim 18, wherein the controller is configured to receiveone or more indications from a proximity sensor, wherein: eachindication is a location of a touch sensed by the proximity sensor in asensing region of the fingerprint sensor; and one or morenon-overlapping portions of the array to be driven for a fingerprintscan correspond to the one or more sensed touches, wherein each of theone or more non-overlapping portions includes a plurality of neighboringcolumns of sensing pixels in the array.
 20. A method of operating a gatedriver for an array of sensing pixels, the method comprising:determining a portion of the array of sensing pixels corresponding toone or more touches in a sensing region of a sensor; driving the sensingpixels of the array in the portion for a scan by the sensor; andpreventing sensing pixels of the array outside the portion from beingdriven.